1. Field of the Invention
The present invention relates to a press processing method and a press processing device, and more specifically to a method and device for processing work by pressing a processing portion against the work at a constant force or torque generated by a constant torque applying means.
2. Description of the Prior Art
Conventionally, the mechanical products or parts are generally chamfered or rounded (referred to as chamfered, simply hereinafter) in order to reduce the stress concentration and to improve the fatigue resistance, the mechanical characteristics, the fitness or engagement characteristics, the assembling characteristics, the external appearance thereof, etc. Here, since this chamfering work needs a skill, the work is often replaced with a robot having a hand to which a grinder is mounted.
Here, whoever, when performed by a grinder mounted on the hand of a multi-joint robot (referred to as robot, simply hereinafter), since this chamfering work must be made by rotating a blade at a low speed and by applying a constant pressure against work to be chamfered, various problems arise due to the characteristics of the multi-joint robot. For instance, since the straight motion of the robot is a zigzag motion when seen microscopically, as shown in FIG. 7, a uniform chamfered surface cannot be obtained. In more detail, in the zigzag motion of the robot arm, when the blade is moved toward work, since the pressing force of the blade increases, the chamfering quantity increases. On the other hand, when the blade is moved away from work, since the pressing force of the blade decreases, the chamfering quantity decreases.
The non-uniformity of the chamfering quantity causes not only a degradation of the external appearance of the products but also a reduction of the strength of the products.
To overcome these problems, various improvement methods have been so far made, when work is chamfered by use of a robot.
For instance, as shown in FIG. 8, Japanese Published Unexamined (Kokai) Patent Application No. 63-196367 has proposed such an automatic chamfering control method that: an electromagnetic variable compliance mechanism d is provided between a wrist a of a robot provided with a locating function and a tool holder c having a chamfering tool b; a displacement gage e and a force sensor f are both arranged at the movable portion of the compliance mechanism d; the tool b is fed in the work w direction by the variable compliance mechanism d; the contact position between the chamfering tool b and the work w is detected by the force sensor f and further stored; the pressing force of the chamfering tool b against the work w is detected by the force sensor f; the variable compliance mechanism d is so controlled that the pressing force can be set to a previously determined set value; the feed rate of the chamfering tool b relative to the work w is detected by the displacement gage e; and the feeding motion of the chamfering tool b is stopped on the basis of the stored contact displacement, whenever the chamfering quantity has reached a predetermined value.
Further, as shown in FIG. 9, Japanese Published Unexamined (Kokai) Patent Application No. 61-109663 has proposed such an automatic profiling method that: when work is polished or ground by a multi-degree-of-freedom robot having a grinder g at its finger end, the rotational torque .tau. of a grinder g is measured by use of a torque meter h or a current value or a rotational speed of a motor m for driving the grinder g; two orthogonal component forces F.sub.1 and F.sub.2 of the grinding resistance force generated during grinding work are measured in the form of moments based upon an arm length x as M.sub.1 =F.sub.1 .multidot.x, and M.sub.2 =F.sub.2 .multidot.x; the spacial coordinates of the contact point between a grinding portion i of the grinder g and the work w and direction ratio of the contact surface are both obtained by a computer j; and the positions and direction of a rod arm k are so controlled that the torque, the spacial coordinates of the contact point, and the contact surface are all set to predetermined values, respectively.
In the above-mentioned prior art methods, however, since the additional procedure of detecting the pressing force of the chamfering tool against work and the rotational toque of the grinder must be both detected and further feedbacked to a robot controller, the control processing is complicated and thereby the processing device is large-sized. As a result, another problem arises in that the installation cost increases. Therefore, there exists a need of a processing method and a processing device, which can achieve the chamfering work under a constant force, without complicating the chamfering method and device.